Systematic Analysis Of The Mechanisms Of QTL CTS-12,a Locus Derived From Guangxi Common Wild Rice In (Oryza Rufipogon Griff.),Mediated Chilling Tolerance In The Rice Seedling Stage

Rice（Oryza sativa L.）is one of major grain crops in the world,but the growth and development of rice are restricted by cold stress.The frequently occurred“spring chill”and“chilling wind”in the rice production areas of middle and lower reaches of the Yangtze river and the south China are to the major causes for the large-scale reduction of rice yield.Compared with cultivated rice,wild rice（Oryza rufipogon Griff.）exhibits higher cold tolerance.Therefore,we aimed at cloning the cold tolerance gene from wild rice and at revealing the molecular mechanism of cold tolerance gene thatare beneficial to the application of cold tolerance gene resources of wild rice to the breeding of new cold-tolerant rice varieties.A Guangxi common wild rice,DP15（chilling tolerant）,and recurrent parental 9311（chilling sensitive）were used to construct a cold-tolerant population in our lab previously.A cold-tolerant QTL,CTS-12 was mapped on rice chromosome 12.In this study,the cold tolerance regulatory mechanism mediated by CTS-12 was systematically studied on physiological,biochemical levels,transcription,and metabolite levels.The results are shown as follows:（1）Under chilling treatment,the expression of chloroplast-related proteins were altered,and the photosynthetic efficiency of 9311 and DC90 were decreased.In recovery,the photosynthesis in DC90 plants could be released from the inhibition under chilling stress.（2）The chilling tolerance of rice is correlated with ABA biosynthesis.The results showed that exogenous application of ABA significantly enhanced the chilling tolerance of 9311 by comparison with the untreated control.Meanwhile,the chilling treated seedlings with the application of Na₂WO₄,an inhibitor of ABA biosynthesis,reduced the chilling tolerance of DC90.The results suggested,the difference content of ABA is one of the main reasons for the chilling stress phenotypes of 9311 and DC90.（3）The reprogramming of transcriptome and metabolome in response to chilling treatment through CTS-12.The integration of transcriptomic and metabolomic dataset were performed by O2PLS and OPLS-DA modeling to investigate the multi-levels of regulation of rice in response to chilling stress.By the analyses of the common and discriminatory DEGs/DEMs,numerous metabolic shifts which were concomitant with the alterations of relevant transcripts were detected in rice plants of both genotypes in response to chilling and recovery stresses,respectively.These mainly included the pathways glycolysis,stachyose biosynthesis,TCA,β-alanine biosynthesis,amino acid metabolism,and ABA biosynthesis and catabolism.The distinct responses of these pathways were observed between chilling and recovery periods.Meanwhile,metabolism of rice plants was differentially re-programmed between 9311 and DC90 to response to different chilling stress.（4）The accumulation of ABA in rice plants in response to chilling treatment.The abundance of ABA synthesis in DC90 plants was significantly higher than that of 9311 plants under chilling stress.Transcriptomic and metabolomic and targeted quantitative analysis of metabolites suggested that ABA involved in the cold stress response of 9311 and DC90 plants,implying that DC90 plants accumulated more ABA content to participate in cold signal transduction,and thereby acquire the stronger chilling tolerances than the 9311.（5）ABA-mediated dynamic balance of water uptake and dissipation in DC90.The enhanced cold tolerance of DC90 plants may be due to the regulation of stomatal closing,the decrease of stomatal density,and thus decreasing transpiration rate to prevent water loss.Under chilling treatment,the stomatal opening and stomatal conductance were affected,however there were no significant differences in the relative water content and water exudation between9311 and DC90.In recovery stage,the relative water content of the leaves of 9311was decreased,and the degree of stomatal opening and the density of the 9311and DC90 were significantly different.Meanwhile,increased endogenous ABA content in plant and accumulation of H₂O₂ in guard cells may be important to the regulation of DC90-regulated stomatal opening and closing.The adjustment of the stomatal opening maintains the balance of water absorption and loss in DC90,so there is no phenomenon of plant death due to cold dehydration under cold stress.（6）There is a possible correlation between endogenous hormones and the chilling tolerance of 9311 and DC90.The analysis of CK,JA,SA,IAA and ACC showed that no significant difference of CK content was observed between 9311and DC90 under chilling treatment,but was observed under recovery.In the chilling treatment,the accumulation level of JA in the cold treatment period of9311 was higher than that of DC90,but ACC,IAA and SA did not change significantly during the cold treatment period.In summary,CTS-12 mediated the different water balance status between9311 and DC90 through ABA.Perturbation of water balance is main reason for chilling sensitive of 9311...